IEEE 802 refers to a family of IEEE standards dealing with Local Area Networks and Metropolitan Area Networks. IEEE 802.11 is a set of medium access control (MAC, or Data Link) layer and physical layer (PHY) specifications for implementing WLAN communication. The 802.11 family is a series of over-the-air modulation techniques that share the same basic protocol. The PHY layer and MAC layer reside in the Open Systems Interconnection (OSI) stack or the OSI 7 layer model, where Layer-1 is known as the PHY layer and Layer-2 is known as the MAC layer.
Functions of PHY layer include converting a MAC layer format suitable to be transported over the medium, adding forward error correction functionality to enable error correction at the receiver, and adding modulation and demodulation modules to incorporate modulation and demodulation functionalities. This will convert bits into symbols for long distance transmission as well as to increase bandwidth efficiency.
The functions of the MAC layer include incorporating a MAC header at the start of upper layer IP packet and cyclic redundancy check (CRC) at the end of IP packet. The MAC header includes a packet length field which helps the receiver know about the total length of packet it is going to receive. The CRC helps in error detections and helps the receiver know whether received packet is erroneous or not. WLAN chipsets and equipment have seen widespread market adoption in recent years. The WLAN market has been mostly driven in the corporate market by the laptop users for its convenience of untethered connectivity, and driven in the home market for home networking purposes such as sharing of broadband connections among multiple PCs. Due to the relatively large power capacity of a laptop computer battery and relatively low expectations from users (typically about 4-6 hours of uninterrupted usage between charges is acceptable), the power consumption of WLAN devices has been relaxed compared with cellular wireless devices.
As the WLAN market matures and the cost of WLAN devices rapidly decreases, there is interest regarding the incorporation of WLAN capability into portable devices, such as cell phones and PDAs. Most of these portable devices are battery powered, and end users generally expect at least a few days of continuous use between battery charges. Power efficiency can thus be important for WLAN devices.